In architecture, the finishing of an underground (UG) water tank is a crucial aspect that ensures durability, water-tightness, and hygiene. Proper finishing involves applying internal plastering with waterproofing additives to prevent seepage and leakage.
The internal surfaces are often treated with a layer of cement-based waterproof coating or epoxy to protect against water contamination and structural degradation. Externally, the tank is typically backfilled with compacted soil after applying a waterproof membrane to protect it from groundwater intrusion.
Good finishing also includes smooth internal surfaces for easy cleaning, rounded corners to avoid dirt accumulation, and proper ventilation and access for maintenance. These measures collectively contribute to the longevity and safe operation of the underground water tank in a building.
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UG water tank finishing detail drawing – 1
A detailed drawing of an underground (UG) water tank finishing in construction typically includes multiple components to ensure water-tightness, structural integrity, and durability. Here’s a breakdown of what should be shown and specified in such a drawing:
UG Water Tank Finishing Detail Drawing Components
Base Slab:
- Material: RCC (M25 or as per structural design).
- Waterproofing: 2 coats of cementitious waterproofing slurry on top surface before wall construction.
- Reinforcement: Detailing of mesh or rebar based on structural load.
Side Walls:
- Material: RCC walls with vertical reinforcement bars.
- Internal Plaster: 12 mm thick cement plaster (1:3) with waterproofing admixture.
- Waterproof Coating: Two coats of brush-applied waterproof slurry (like SikaTop Seal, Dr. Fixit, etc.).
- Fillet Joint: 75 mm × 75 mm cement fillet at wall-to-floor junctions to prevent leakage.
- External Waterproofing: Bituminous membrane or PU-based liquid membrane applied before backfilling.
Top Slab (if applicable):
- Access: Cast-in-situ RCC slab with manhole openings for maintenance.
- Vent Pipes: Provided with mosquito mesh to allow air circulation and prevent contamination.
- Waterproofing: Similar treatment as walls; internal plastering and coating.
Inlet, Outlet & Overflow Pipes:
- Pipe Sealing: Use of puddle flanges or gunite seals at pipe penetrations to avoid leakage.
- Materials: uPVC or GI pipes as per specification.
Backfilling:
- Protection Board: 10 mm thick protection board over external membrane.
- Layering: Compacted sand cushion followed by selected soil fill in layers.
- Weep Holes: If needed, for groundwater relief during construction (temporarily plugged later).
Surface Finishing (Inside):
- Smooth Finish: Cement float finish for hygienic surface.
- Rounded Corners: For easy cleaning and to avoid algae growth.
- Non-toxic Coating: Optional food-grade epoxy for potable water tanks.
Drawing Notes (on sheet):
- All waterproofing materials should be approved and tested before application.
- All construction joints must be treated with water bars (PVC or hydrophilic).
- Concrete curing to be done as per IS standards.
- Ensure slope of base slab (1:100) toward sump/pump inlet for complete drainage.
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